﻿/*
* Copyright 2007 ZXing authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*      http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
using System;
using com.google.zxing;
using com.google.zxing.common;

namespace com.google.zxing.qrcode.detector
{
    public sealed class AlignmentPatternFinder
    { 
          private  MonochromeBitmapSource image;
          private  System.Collections.ArrayList possibleCenters;
          private  int startX;
          private  int startY;
          private  int width;
          private  int height;
          private  float moduleSize;
          private  int[] crossCheckStateCount;

          /**
           * <p>Creates a finder that will look in a portion of the whole image.</p>
           *
           * @param image image to search
           * @param startX left column from which to start searching
           * @param startY top row from which to start searching
           * @param width width of region to search
           * @param height height of region to search
           * @param moduleSize estimated module size so far
           */
          public AlignmentPatternFinder(MonochromeBitmapSource image,
                                 int startX,
                                 int startY,
                                 int width,
                                 int height,
                                 float moduleSize) {
            this.image = image;
            this.possibleCenters = new System.Collections.ArrayList(5);
            this.startX = startX;
            this.startY = startY;
            this.width = width;
            this.height = height;
            this.moduleSize = moduleSize;
            this.crossCheckStateCount = new int[3];
          }

          /**
           * <p>This method attempts to find the bottom-right alignment pattern in the image. It is a bit messy since
           * it's pretty performance-critical and so is written to be fast foremost.</p>
           *
           * @return {@link AlignmentPattern} if found
           * @throws ReaderException if not found
           */
          public AlignmentPattern find() {
            int startX = this.startX;
            int height = this.height;
            int maxJ = startX + width;
            int middleI = startY + (height >> 1);
            BitArray luminanceRow = new BitArray(width);
            // We are looking for black/white/black modules in 1:1:1 ratio;
            // this tracks the number of black/white/black modules seen so far
            int[] stateCount = new int[3];
            for (int iGen = 0; iGen < height; iGen++) {
              // Search from middle outwards
              int i = middleI + ((iGen & 0x01) == 0 ? ((iGen + 1) >> 1) : -((iGen + 1) >> 1));
              image.getBlackRow(i, luminanceRow, startX, width);
              stateCount[0] = 0;
              stateCount[1] = 0;
              stateCount[2] = 0;
              int j = startX;
              // Burn off leading white pixels before anything else; if we start in the middle of
              // a white run, it doesn't make sense to count its length, since we don't know if the
              // white run continued to the left of the start point
              while (j < maxJ && !luminanceRow.get(j - startX)) {
                j++;
              }
              int currentState = 0;
              while (j < maxJ) {
                if (luminanceRow.get(j - startX)) {
                  // Black pixel
                  if (currentState == 1) { // Counting black pixels
                    stateCount[currentState]++;
                  } else { // Counting white pixels
                    if (currentState == 2) { // A winner?
                      if (foundPatternCross(stateCount)) { // Yes
                        AlignmentPattern confirmed = handlePossibleCenter(stateCount, i, j);
                        if (confirmed != null) {
                          return confirmed;
                        }
                      }
                      stateCount[0] = stateCount[2];
                      stateCount[1] = 1;
                      stateCount[2] = 0;
                      currentState = 1;
                    } else {
                      stateCount[++currentState]++;
                    }
                  }
                } else { // White pixel
                  if (currentState == 1) { // Counting black pixels
                    currentState++;
                  }
                  stateCount[currentState]++;
                }
                j++;
              }
              if (foundPatternCross(stateCount)) {
                AlignmentPattern confirmed = handlePossibleCenter(stateCount, i, maxJ);
                if (confirmed != null) {
                  return confirmed;
                }
              }

            }

            // Hmm, nothing we saw was observed and confirmed twice. If we had
            // any guess at all, return it.
            if (!(possibleCenters.Count==0)) {
              return (AlignmentPattern) possibleCenters[0];
            }

            throw new ReaderException();
          }

          /**
           * Given a count of black/white/black pixels just seen and an end position,
           * figures the location of the center of this black/white/black run.
           */
          private static float centerFromEnd(int[] stateCount, int end) {
            return (float) (end - stateCount[2]) - stateCount[1] / 2.0f;
          }

          /**
           * @param stateCount count of black/white/black pixels just read
           * @return true iff the proportions of the counts is close enough to the 1/1/1 ratios
           *         used by alignment patterns to be considered a match
           */
          private bool foundPatternCross(int[] stateCount) {
            float moduleSize = this.moduleSize;
            float maxVariance = moduleSize / 2.0f;
            for (int i = 0; i < 3; i++) {
              if (Math.Abs(moduleSize - stateCount[i]) >= maxVariance) {
                return false;
              }
            }
            return true;
          }

          /**
           * <p>After a horizontal scan finds a potential alignment pattern, this method
           * "cross-checks" by scanning down vertically through the center of the possible
           * alignment pattern to see if the same proportion is detected.</p>
           *
           * @param startI row where an alignment pattern was detected
           * @param centerJ center of the section that appears to cross an alignment pattern
           * @param maxCount maximum reasonable number of modules that should be
           * observed in any reading state, based on the results of the horizontal scan
           * @return vertical center of alignment pattern, or {@link Float#NaN} if not found
           */
          private float crossCheckVertical(int startI, int centerJ, int maxCount, int originalStateCountTotal) {
            MonochromeBitmapSource image = this.image;

            int maxI = image.getHeight();
            int[] stateCount = crossCheckStateCount;
            stateCount[0] = 0;
            stateCount[1] = 0;
            stateCount[2] = 0;

            // Start counting up from center
            int i = startI;
            while (i >= 0 && image.isBlack(centerJ, i) && stateCount[1] <= maxCount) {
              stateCount[1]++;
              i--;
            }
            // If already too many modules in this state or ran off the edge:
            if (i < 0 || stateCount[1] > maxCount) {
              return float.NaN;
            }
            while (i >= 0 && !image.isBlack(centerJ, i) && stateCount[0] <= maxCount) {
              stateCount[0]++;
              i--;
            }
            if (stateCount[0] > maxCount) {
                return float.NaN;
            }

            // Now also count down from center
            i = startI + 1;
            while (i < maxI && image.isBlack(centerJ, i) && stateCount[1] <= maxCount) {
              stateCount[1]++;
              i++;
            }
            if (i == maxI || stateCount[1] > maxCount) {
                return float.NaN;
            }
            while (i < maxI && !image.isBlack(centerJ, i) && stateCount[2] <= maxCount) {
              stateCount[2]++;
              i++;
            }
            if (stateCount[2] > maxCount) {
                return float.NaN;
            }

            int stateCountTotal = stateCount[0] + stateCount[1] + stateCount[2];
            if (5 * Math.Abs(stateCountTotal - originalStateCountTotal) >= originalStateCountTotal) {
                return float.NaN;
            }

            return foundPatternCross(stateCount) ? centerFromEnd(stateCount, i) : float.NaN;
          }

          /**
           * <p>This is called when a horizontal scan finds a possible alignment pattern. It will
           * cross check with a vertical scan, and if successful, will see if this pattern had been
           * found on a previous horizontal scan. If so, we consider it confirmed and conclude we have
           * found the alignment pattern.</p>
           *
           * @param stateCount reading state module counts from horizontal scan
           * @param i row where alignment pattern may be found
           * @param j end of possible alignment pattern in row
           * @return {@link AlignmentPattern} if we have found the same pattern twice, or null if not
           */
          private AlignmentPattern handlePossibleCenter(int[] stateCount, int i, int j) {
            int stateCountTotal = stateCount[0] + stateCount[1] + stateCount[2];
            float centerJ = centerFromEnd(stateCount, j);
            float centerI = crossCheckVertical(i, (int) centerJ, 2 * stateCount[1], stateCountTotal);
            if (!Single.IsNaN(centerI))
            {
              float estimatedModuleSize = (float) (stateCount[0] + stateCount[1] + stateCount[2]) / 3.0f;
              int max = possibleCenters.Count;
              for (int index = 0; index < max; index++) {
                AlignmentPattern center = (AlignmentPattern) possibleCenters[index];
                // Look for about the same center and module size:
                if (center.aboutEquals(estimatedModuleSize, centerI, centerJ)) {
                  return new AlignmentPattern(centerJ, centerI, estimatedModuleSize);
                }
              }
              // Hadn't found this before; save it
              possibleCenters.Add(new AlignmentPattern(centerJ, centerI, estimatedModuleSize));
            }
            return null;
          }
    
    
    }
}